1. Field of the Invention
The invention pertains generally to methods and apparatus relating to sensor systems.
2. Description of Related Art
For highly sensitive sensors, such as space-viewing sensors and missile defense infrared sensors, the system's ability to see targets may be limited by emissions from warm surfaces within the sensor's optical system. For example, in telescope-type systems, a secondary mirror is held relative to a primary mirror using mechanical struts that are within the sensor's collecting aperture. Traditionally, struts are painted black and are highly emissive and warm, generating a high thermal background contribution. Infrared sensors, however, operate more effectively with minimal thermal self-emission from the sensor and surrounding components reaching the focal plane array (FPA) or other detectors. The geometry around and holding the FPA is typically cooled to minimize the thermal self-emission, but the struts are not, and therefore are visible to the FPA. The strut blocks part of the sensor's collecting aperture and reflection or emission of light by struts may cause the FPA to view warm parts of the sensor and sense significant thermal background.
Newer strut designs use a highly reflective stair-step design that are used to view cold surfaces or outer space. These struts have low emissivity, so the thermal background from struts can be greatly reduced using stair steps. For sensors using advanced composite materials for their mirrors and mounts, however, struts with a stair-step pattern cannot be easily manufactured, as machining sharp corners fractures the brittle composite. Alternative designs, such as an L-shaped strut, occupy significant space.